The present invention relates to a pump such as a hydraulic pump, and particularly to a pump that maintains balanced axial forces on the pumping mechanism, even in the event of high inlet and outlet pump pressures.
The hydraulic system disclosed in Tieben U.S. Pat. No. 5,916,139 includes a pump, an actuator and a reservoir. In one mode of operation, the pump inlet is connected to the reservoir and the pump outlet is connected to the actuator. In another mode of operation, the pump inlet is connected to the actuator and the pump outlet is connected to the reservoir. This system encounters relatively high fluid pressures at both the pump inlet and the pump outlet. As explained in the Tieben patent, such pressures can result in undesired axial loads on the pumping mechanism, due to the high internal pressure of the pump. The pump disclosed in the Tieben patent overcomes this potential problem by providing high-pressure seals at both ends of the driven shaft of the pump. In this way, hydraulic axial forces on the driven shaft are balanced, and friction and associated wear are reduced.
One potential drawback of the pump illustrated in the Tieben patent is that two high-pressure shaft seals are required. Furthermore, under some conditions cup seals of the type illustrated in the Tieben patent can cause wear on the sealed shaft and associated leaks.
The present invention is directed to an improved pump that is well-suited for use in applications having high internal pump pressures and that overcomes the potential disadvantages described above.